Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session K26: Chemical Physics of Hydrogen Bonding IV |
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Sponsoring Units: DCP Chair: Huib Bakker, AMOLF, The Netherlands Room: 289 |
Wednesday, March 15, 2017 8:00AM - 8:12AM |
K26.00001: Water confined between hydrophobic and hydrophilic plates Zhenghan Gao, Nicolas Giovambattista, Ozgur Sahin Water remains stable under tension due to its cohesion. For bulk water, experiments show it can remain stable down to -120Mpa. However, confinement can change the stability of the systems and may affect the phase diagram. For example, water confined in graphene can form square ice at room temperature. Using molecular dynamic simulation, we investigate the phase diagram of water and its physical states when water is confined between graphene sheets. Our results allowed determining pressure-separation phase diagrams of water confined by hydrophobic and hydrophilic surfaces. Although water under confinement is difficult to study experimentally, our MD simulations offer insight into the basic features of these systems. [Preview Abstract] |
Wednesday, March 15, 2017 8:12AM - 8:24AM |
K26.00002: Structural characterizations of water-metal interfaces with large-scale first principles molecular dynamics Kevin Ryczko, Isaac Tamblyn We analyze and compare the structural, dynamical, and electronic properties of liquid water next to prototypical metals including Pt, graphite, and graphene. Our analysis is built on Born-Oppenheimer molecular dynamics (BOMD) generated using density functional theory (DFT). All calculations we present use large simulation cells, allowing for an accurate treatment of the water-electrode interfaces. We have included van der Waals (vdW) interactions through the use of the optB86b-vdW exchange correlation functional, as it includes non-local interactions and has shown to give good results with respect to structural experiments. Comparisons with the Perdew-Burke-Ernzerhof (PBE) exchange correlation functional are also shown. We find an initial peak, due to chemisorption, in the density profile of the liquid water-Pt interface not seen in the liquid water-graphite interface, liquid water-graphene interface, nor interfaces covered in other literature. To further investigate this chemisorption peak we also report differences between single water adsorption on the Pt and graphite surfaces. In total, over 135 ps of BOMD data was generated and analyzed. [Preview Abstract] |
Wednesday, March 15, 2017 8:24AM - 8:36AM |
K26.00003: Dynamics of N-methylacetamide in methanol via ab initio molecular dynamics Vivek K. Yadav, Michael L. Klein There has been much interest in the two-dimensional infrared (2D IR) amide 1 vibrational bands of proteins as well as molecules such as N-methylacetamide (NMA), which present peptide-like H-bonding possibilities to a solvent. To assist in rationalizing a large body of experimental 2D IR data on NMA in both aqueous and non-aqueous solvents, we have performed an ab initio molecular dynamics simulation of NMA in methanol. The trajectory was generated using ab initio molecular dynamics. The AIMD simulation is performed at a $\sim$ 30K elevated temperature in order to roughly account for the structural softening of hydrogen bonds that arise from nuclear quantum effects. The calculated average hydrogen bond lifetime for the amide mode I frequency is $\sim$ 1.9 ps which are in good agreement with the classical theoretical and experimental results. Our calculated bulk methanol-methanol hydrogen bond lifetime also matched with the experimental findings. We theoretically performed 2D IR where the change in spectral shape with respect to time is directly influenced by the decay of the frequency-frequency correlations, which represents a desired experimental property. [Preview Abstract] |
Wednesday, March 15, 2017 8:36AM - 8:48AM |
K26.00004: Predicting the electronic properties of aqueous solutions from first-principles Eric Schwegler, Tuan Anh Pham, Marco Govoni, Robert Seidel, Stephen Bradforth, Giulia Galli Predicting the electronic properties of aqueous liquids has been a long-standing challenge for quantum-mechanical methods. Yet it is a crucial step in understanding and predicting the key role played by aqueous solutions and electrolytes in a wide variety of emerging energy and environmental technologies, including battery and photoelectrochemical cell design. Here we propose an efficient and accurate approach to predict the electronic properties of aqueous solutions, based on the combination of first-principles methods and experimental validation using state-of-the-art spectroscopic measurements. We present results for the photoelectron spectra of a broad range of solvated ions, showing that first-principles molecular dynamics simulations and electronic structure calculations using dielectric hybrid functionals provide a quantitative description of their electronic properties, including excitation energies, of the solvent and solutes. The proposed computational framework is general and applicable to other liquids, thereby offering great promise in understanding and engineering solutions and liquid electrolytes for a variety of important energy technologies. [Preview Abstract] |
Wednesday, March 15, 2017 8:48AM - 9:00AM |
K26.00005: Wetting transitions in alkane-water systems for nanodroplets and planar interfaces Pauf Neupane, Fawaz Hrahsheh, Gerald Wilemski The temperature dependent wetting behavior of alkanes on water is studied using molecular dynamics simulations for SPC/E water and unified atom 6-12 Lennard-Jones (LJ) alkane models. Water-alkane interactions are modeled using a LJ potential with energy and size parameters adjusted to reproduce experimentally observed wetting behavior for nonane at 295 K. For reasonable values of the LJ parameters, core-shell structures of water-nonane nanodroplets are observed at low temperatures, $T$ \textless 250 K, indicating that nonane perfectly wets SPC/E water with a zero contact angle at low temperatures. At higher $T$, imperfect wetting is found as a nonane lens forms on the water drop with a finite, non-zero contact angle yielding a Russian Doll structure. For planar alkane-water interfaces, our simulation results are consistent with the occurrence of low temperature and high temperature wetting transitions. Within the imperfect wetting region at low temperature, the contact angle formed by alkanes on water initially increases with temperature until a maximum dewetting temperature (MDT) is reached. Beyond the MDT, the contact angle decreases as the system approaches the usual high temperature wetting transition. The imperfect wetting temperature range decreases with reducing alkane chain length. [Preview Abstract] |
Wednesday, March 15, 2017 9:00AM - 9:12AM |
K26.00006: Qualitative differences between simulations and experiments of confined glasses Robert Riggleman, Yue Zhang, Zahra Fakhraai After two decades of experimental and computational work, it is widely accepted that nanoscale confinement strongly perturbs the dynamics associated with glass formation. The presence of either a free surface or a non-wetting wall leads to a local enhancement of the dynamics, while strongly absorbing walls can slow the dynamics of glass formers. These qualitative trends have been observed in experiments through both direct and indirect measures of the dynamics, and simulations that directly measure the local mobility exhibit similar trends. However, there are several experimental observations that are qualitatively different from what is observed in simulations. In this talk, I will highlight these apparent discrepancies as well as describe our attempts at resolving them. I will compare the specific form of relaxation functions, which exhibit a broad single-step decay in simulations but two-step relaxation in several experiments. Finally, I will examine the activation energy for relaxation as a function of film thickness and compare to recent experiments that exhibit a strong crossover in the dynamics when the film thickness is approximately 25 nm. [Preview Abstract] |
Wednesday, March 15, 2017 9:12AM - 9:24AM |
K26.00007: Accuracy of Density Functional Theory to Predict Vapor-Liquid Equilibria Neeraj Rai, Himanshu Goel, Zachary Windom, Charles Butler, Amber Jackson, Anna Taconi, Breanna Ellis Sorption and phase equilibria is central to numerous separation processes such as ammonia production, acid gas removal from flue gases, and petroleum refining. However, a fundamental understanding of these processes is severely lacking due to our inability to probe these systems at the molecular scale to elucidate sorption mechanism. Recent developments and implementation of novel Monte Carlo algorithms in CP2K software suite allow one to combine first principles approach to compute the system energies, and Gibbs ensemble Monte Carlo technique to model sorption and phase equilibria. Here, we use density functional theory at different levels of approximations to calculate vapor liquid equilibria of weakly interacting systems that are dominated by dispersion interactions. Our results indicate that use of dispersion correction scheme (D3) with GGA functionals perform better than rVV10 nonlocal density functional. [Preview Abstract] |
Wednesday, March 15, 2017 9:24AM - 9:36AM |
K26.00008: Structural and functional analysis of glycoprotein butyrylcholinesterase using atomistic molecular dynamics Austen Bernardi, Roland Faller Atomistic molecular dynamics (MD) has proven to be a powerful tool for studying the structure and dynamics of biological systems on nanosecond to microsecond time scales and nanometer length scales. In this work we study the effects of modifying the glycan distribution on the structure and function of full length monomeric butyrylcholinesterase (BChE). BChE exists as a monomer, dimer, or tetramer, and is a therapeutic glycoprotein with nine asparagine glycosylation sites per monomer. Each monomer acts as a stoichiometric scavenger for organophosphorus (OP) nerve agents (e.g. sarin, soman). Glycan distributions are highly heterogeneous and have been shown experimentally to affect certain glycoproteins' stability and reactivity. We performed structural analysis of various biologically relevant glycoforms of BChE using classical atomistic MD. Functional analysis was performed through binding energy simulations using umbrella sampling with BChE and OP cofactors. Additionally, we assess the quality of the glycans' conformational sampling. We found that the glycan distribution has a significant effect on the structure and function of BChE on timescales available to atomistic MD. [Preview Abstract] |
Wednesday, March 15, 2017 9:36AM - 9:48AM |
K26.00009: Multiscale modeling for confined fluids in open framework materials. Jianzhong Wu Open framework materials are a special class of crystalline solids that can be synthesized via modular construction from a wide variety of organic linkers and organometallic or nonmetallic nodes. Whereas enormous developments have been reported in recent years for in silico design of these nanostructure materials with predictable crystallographic topology, accurate prediction of the equilibrium and transport properties of gases and liquids in the micropores of such materials remains a daunting challenge. In this presentation, I will summarize our recent efforts toward developing multiscale procedures that enable customized modeling of confined fluids in open framework materials. Our theoretical development leverages recent advances in applications of quantum and statistical mechanical methods, in particular those based on the density functional theory, to predict the electronic structure, intermolecular interactions, and macroscopic properties of the complex heterogeneous systems. [Preview Abstract] |
Wednesday, March 15, 2017 9:48AM - 10:00AM |
K26.00010: Molecular insights into early stage aggregation of di-Fmoc-L-lysine in binary mixture of organic solvent and water Md Masrul Huda, Neeraj Rai Molecular gels are relatively new class of soft materials, which are formed by the supramolecular aggregation of low molecular weight gelators (LMWGs) in organic solvents and/or water. Hierarchical self-assembly of small gelator molecules lead to three-dimensional complex fibrillar networks, which restricts the flow of solvents and results in viscous solid like materials or gels. These gels have drawn significant attentions for their potential applications for drug delivery, tissue engineering, materials for sensors etc. As of now, self-assembly of gelator molecules into one-dimensional fibers is not well understood, although that is very important to design new gelators for desired applications. Here, we present molecular dynamics study that provides molecular level insight into early stage aggregation of selected gelator, di-Fmoc-L-lysine in binary mixture of organic solvent and water. We will present the role of different functional groups of gelator molecule such as aromatic ring, amide, and carboxylic group on aggregation. We will also present the effect of concentrations of gelator and solvent on self-assembly of gelators. This study has captured helical fiber growth and branching of fiber, which is in good agreement with experimental observations. [Preview Abstract] |
Wednesday, March 15, 2017 10:00AM - 10:12AM |
K26.00011: Structural and Physical Properties of Ionic Liquid Mixtures Seoncheol Cha, Doseok Kim Ionic liquids are the materials consisting of only cations and anions and existing at liquid phase below 100~°C. They are called “designer solvent” as the physical properties of the materials can be tuned by changing their constituent ions. Mixing ionic liquids is a new way of maximizing this advantage because the material properties can be changed continuously in the mixture. The excess molar volumes, a difference between the molar volumes of the mixtures and a linear interpolation between the volumes of pure components, have been found to differ significantly for some ionic liquid mixtures, but the origin of this difference is not well understood. The different microstructures of the mixtures, which can range from a simple mixture of two different consisting ionic liquids to a different structure from those of pure materials, have been suggested as the origin of this difference. We investigated ionic liquid mixture systems by IR spectroscopy by utilizing a particular peak in the IR spectrum for the moiety participating in the hydrogen bonding ($\nu $C(2)-H) that changes sensitively with the change of the anion in the ionic liquid. The absorbance of $\nu $C(2)-H changed proportionally to the composition for the mixtures consisting of halide anion. By contrast, the absorbance changed nonlinearly for the mixtures of which one of the anion had multiple interaction sites [Preview Abstract] |
Wednesday, March 15, 2017 10:12AM - 10:24AM |
K26.00012: Cl- solution studied by \textit{ab initio} molecular dynamics considering nuclear quantum effect on proton Zhaoru Sun, Mohan Chen, Xifan Wu The H-bond structure perturbed by solvated ions of the Hofmeister series is a topic of great interest in many biological, biochemical and electrochemical process. In classical \textit{ab initio} molecular dynamics (AIMD) simulations, the Cl- , a representative ion, does not significantly affect the structure of water for dilute solution with salt concentration below 1M. Recently, it is found that nuclear quantum effect (NQE) has significant influence on the hydrogen bond in pure water by softening the H-bond. By considering the NQE on proton in both dilute Cl- solution and pure liquid water using path integral molecular dynamics with colored noise thermostat, we find that the oxygen-oxygen radial distribution functions in Cl- solution is over-structured than that in pure water, indicating that the hydrogen bond in Cl- solution becomes stronger. We will validate our finding by the analysis of solvation structure change, Wannier center distribution and dipole moment of water. Our work shows that NQE cannot be neglected for the hydrogen bond network in Hofmeister ion solutions. [Preview Abstract] |
Wednesday, March 15, 2017 10:24AM - 10:36AM |
K26.00013: Retardation of Bulk Water Dynamics by Disaccharide Osmolytes Nimesh Shukla, Lee Chen, Enrico Pomarico, Majed Chergui, Christina Othon Bioprotective nature of disaccharides is hypothesized to derive from the modification of the hydrogen bonding network of water which protects biomolecules through lowered water activity at the protein interface. Using ultrafast fluorescence spectroscopy, we measured the relaxation of bulk water dynamics around the induced dipole moment of two fluorescent probes (Lucifer Yellow Ethylenediamine and Tryptophan). Our results indicate a reduction in bulk water reorganization rate of approximately 30{\%}. We observe this retardation in the low concentration regime measured at 0.1 and 0.25 M, far below the onset of glassy dynamics. This water structuring should be significant in crowded biological systems, contributing to a global change in protein energy landscape, resulting in a significant enhancement of protein stability under environmental stress. We observed similar dynamic reduction for two disaccharide osmolytes, sucrose and trehalose, with trehalose being the more effective in reducing solvation dynamics. [Preview Abstract] |
Wednesday, March 15, 2017 10:36AM - 10:48AM |
K26.00014: Two different ground states in K-doped polyacenes satoshi heguri, Quynh Phan Thi Nhu, hiroyuki tamura, takehito nakano, yasuo nozue, katsumi tanigaki The electronic states of potassium (K) doped zigzag-type polycyclic aromatic hydrocarbon (polyacenes (PLAs)) K$_{x}$(PLAs), are studied for a series of the four smallest molecules: naphthalene (NN), anthrance (AN), tetracene (TN), and pentacene (PN), focusing on their 1:1 stoichiometric phases. Clear experimental differences are identified between the first group (K$_{1}$(NN) and K$_{1}$(AN)) and the second group (K$_{1}$(TN) and K$_{1}$(PN)) by magnetic, vibrational, and optical measurements. The first group is categorized as a Mott insulator with an antiferromagnetic ground state with energy of c.a. 10 meV, while the second group is classified as a band insulator via dimer formation due to the spin Peierls instability. In the latter system, the first thermally accessible triplet states are located far apart from the singlet ground states at room temperature, and are not detected by electron spin resonance spectroscopy until 300 K, being very different from what is observed for hole doped PN reported earlier. The results give a new systematic understanding on the electronic states of electron doped PLAs sensitive to the energetic balance among on-site Coulomb repulsion, band width and the Peierls instability. [Preview Abstract] |
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